Several documents are known from the prior art, describing systems for measuring acoustic non-linearity. These publications describe methods for measuring non-linear acoustic effects by subjecting the tested material to mechanical stresses of variable amplitude. In fact, application of variable mechanical stress to the tested material modifies its elastic, and sometimes dissipative, properties.
Part of these methods measures variations in propagation and amplitude speed of acoustic waves in a sample, caused by a quasi-static variation in the state of mechanical stress (hydrostatic pressure or uniaxial stress) of this sample. The other part of these methods uses the interaction of two acoustic waves and in general measures the growth of harmonics of the low-frequency wave:                N. Ichida, T. Sato, M. Linzer; Imaging the nonlinear parameter of the medium, Ultrason. Imaging, Vol. 5, 1983; pp. 295-299.        Z. Zhu, M. S. Roos, W. N. Cobb, K. Jensen; Determination of the acoustic nonlinearity parameter B/A from phase measurements; J. Acoust. Soc. Am., Vol. 74(5), 1983; pp. 1518-1521;        C. Barriere, D. Royer; Diffraction effects in the parametric interaction of acoustic waves: application to measurements of the nonlinearity parameter B/A in liquids; IEEE Trans. UFFC, Vol. 48 (6), 2001, pp. 1706-1715;        C M. Sehgal, R. C Bahn, J. F. Greenleaf; Measurement of the acoustic nonlinearity parameter B/A in human tissues by a thermodynamic method; J. Acoust. Am. Soc, Vol. 76(4), 1984; pp. 1023-1029;        V. Zaitsev, V. Nazarov, V. Gusev and B. Castagnede; Novel nonlinear modulation acoustic technique for crack detection; NDT&E International, 39 (2006) 184-194;        G. Gremaud, M. Bujard, and W. Benoit; The coupling technique: A two-acoustic wave method for the study of dislocation dynamics; J. Appl. Phys. 1987 61(5), 1795-1805.        
However, such measuring systems have a number of disadvantages:    Techniques utilising a quasi-static test machine (needing contacting of the sample with the device) are not applicable to fluid media, gels and to living media (biomedical applications in vivo). Those dry-medium methods needing contact (adhesion for example) of the ultrasound transducers with the samples, and thus altering their surfaces, are not compatible with some applications, especially biomedical applications. Those methods employing an ultrasound wave emitted continuously can generate stationary waves complexing measurement analysis.
In the case of collinear interaction between the low-frequency wave and the ultrasound wave, there can be zones of acoustic shade in the low-frequency field created by ultrasound transducers. Those methods employing collinear interaction between the low-frequency wave and the ultrasound wave, and where the ultrasound wave must complete one or more return trips in the sample, are applicable to sharply attenuating media such as osseous tissue. Those methods employing a mechanical device in contact for varying stresses in the sample, without using mechanical resonance of this sample, have a limited range of use in terms of deformation speed (at most a few kHz).
Those methods employing a mechanical device in contact for varying stresses in the sample, using mechanical resonance of this sample, can reach deformation frequencies of a few tens of kHz, however the mechanical resonance frequency is conditioned by the geometric dimensions and the physical properties of the sample. Those methods varying the hydrostatic pressure by bearings and needing to enclose the tested sample in a hermetically sealed enclosure filled with liquid have a relatively complex conception and usage.
Those methods, not utilising a low-frequency acoustic wave to generate variations in stress, experience difficulty in conducting a test in compression and traction at the same time (or compression and relief). In the case of test machines, the holding device alters the sample. In the case of hermetically sealed enclosures, a drop in hydrostatic pressure less than atmospheric pressure requires relatively complex conception.